Having another problem - 'Cannot call unknown function', but the function exists #22974

inhahe · 2024-11-20T20:41:13Z

inhahe
Nov 20, 2024

Here's my HTML:

<!DOCTYPE html>
<html>
  <head>
      <meta charset="utf-8">
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  </head>
  <body>
    <!-- Create the canvas that the C++ code will draw into -->
    <canvas id="canvas" oncontextmenu="event.preventDefault()"></canvas>

    <!-- Allow the C++ to access the canvas element -->
    <script type='text/javascript'>
      var Module = {
        canvas: (function () { return document.getElementById('canvas'); })()
      };
    </script>

    <script>
      Module.onRuntimeInitialized = () =>
      {
        console.log(...Object.keys(Module)); // Lists all exported functions and variables
        const pixelsptr = Module.ccall(_getpixels, 'number', [], []);
      };
    </script>

    <!-- Add the javascript glue code (index.js) as generated by Emscripten -->
    <script src="em.js"></script>

  </body>
</html>

Here's the relevant C++ lines:

static uint8_t pixels[w * h * 4];
extern "C" {uint8_t* EMSCRIPTEN_KEEPALIVE getpixels() { return &pixels[0]; }}

Here's my em++ command line:
em++ /mnt/d/visual\ studio\ projects/scribbles3/em.cpp -s WASM=1 -s -o em.js -sALLOW_MEMORY_GROWTH -Oz -sEXPORTED_FUNCTIONS=_getpixels,_mainloop,_main -sEXPORTED_RUNTIME_METHODS=ccall,cwrap -s ASSERTIONS=2
Here's my console output:

em.js:1 Aborted(Assertion failed: Cannot call unknown function (...args)=>{assert(runtimeInitialized,`native function \`${name}\` called before runtime initialization`);var f=wasmExports[name];assert(f,`exported native function \`${name}\` not found`);assert(args.length<=nargs,`native function \`${name}\` called with ${args.length} args but expects ${nargs}`);return f(...args)}, make sure it is exported)
abort @ em.js:1
em.js:1 Uncaught (in promise) RuntimeError: Aborted(Assertion failed: Cannot call unknown function (...args)=>{assert(runtimeInitialized,`native function \`${name}\` called before runtime initialization`);var f=wasmExports[name];assert(f,`exported native function \`${name}\` not found`);assert(args.length<=nargs,`native function \`${name}\` called with ${args.length} args but expects ${nargs}`);return f(...args)}, make sure it is exported)
    at abort (em.js:1:10513)
    at assert (em.js:1:5912)
    at getCFunc (em.js:1:26423)
    at Object.ccall (em.js:1:27085)
    at Module.onRuntimeInitialized (monkey_test.html:22:34)
    at doRun (em.js:1:35873)
    at run (em.js:1:36050)
    at runCaller (em.js:1:34923)
    at removeRunDependency (em.js:1:10401)
    at receiveInstance (em.js:1:13705)

As you can see, '_getpixels' is actaully listed in the module's contents, and it also shouldn't run before it's initialized, despite what it says, because it runs under `onRuntimeInitialized'.

sbc100 · 2024-11-20T21:59:35Z

sbc100
Nov 20, 2024
Maintainer

The ccall function expects a string as its first argument, not a function. So you would do ccall('getpixels') (also note that you don't need that leading underscore here).

Also, if you do EMSCRIPTEN_KEEPALIVE you don't also need to add it to EXPORTED_FUNCTIONS (those two things have the same effect).

4 replies

inhahe Nov 20, 2024
Author

The ccall function expects a string as its first argument, not a function. So you would do ccall('getpixels') (also note that you don't need that leading underscore here).

Also, if you do EMSCRIPTEN_KEEPALIVE you don't also need to add it to EXPORTED_FUNCTIONS (those two things have the same effect).

Thanks, I'll try that. For some reason the docs didn't seem to explain or give an example of how to use ccall, that I remember.

Regarding keepalive and exported_functions, I had just the EMSCRIPTEN_KEEPALIVE and it didn't export them. I guess you mean EXPORTED_FUNCTIONS also implies EMSCRIPTEN_KEEPALIVE but not vice versa

sbc100 Nov 20, 2024
Maintainer

EMSCRIPTEN_KEEPALIVE implies EXPORTED_FUNCTIONS.. thats really all it does

sbc100 Nov 20, 2024
Maintainer

The docs for ccall and cwap do you strings: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#calling-compiled-c-functions-from-javascript-using-ccall-cwrap. Although maybe we should add more assertions if its confusing.

inhahe Nov 20, 2024
Author

The docs for ccall and cwap do you strings: https://emscripten.org/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.html#calling-compiled-c-functions-from-javascript-using-ccall-cwrap. Although maybe we should add more assertions if its confusing.

Oh, yes, I see it does say how to use ccall. I guess I just overlooked the first parameter! duh. thanks.

I guess I should have known '_getpixels' wouldn't be in the global namespace, i must not have noticed i forgot the quotes.

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Having another problem - 'Cannot call unknown function', but the function exists #22974

inhahe Nov 20, 2024

Replies: 1 comment · 4 replies

sbc100 Nov 20, 2024 Maintainer

inhahe Nov 20, 2024 Author

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sbc100 Nov 20, 2024 Maintainer

inhahe Nov 20, 2024 Author

inhahe
Nov 20, 2024

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sbc100
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inhahe Nov 20, 2024
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sbc100 Nov 20, 2024
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sbc100 Nov 20, 2024
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inhahe Nov 20, 2024
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